Molecular Development - X Inactivation
Introduction
The presence in females of 2 X chromosome raises the issue of gene dosage, in the case of mammals this is regulated by inactivating one of the X chromosomes (see X inactivation notes). In some other species compensation occurs by increasing the expression of X in males. The pattern of which X chromosome is inactivated in cells appears to be random, generating 50% cells expressing Father X, 50% cells expressing Mother X (mosaic pattern). The theory of random X inactivation was first suggested in mice in 1961.
A second form of X inactivation that occurs only in male meiotic spermatogenesis, meiotic sex chromosome inactivation (MSCI), is not covered in these current notes. MSCI is the process of transcriptional silencing of the X and Y chromosomes. (More? Meiotic sex chromosome inactivation. Turner JM. Development. 2007 May;134(10):1823-31.)
Some Recent Findings
- Variations of X chromosome inactivation occur in early passages of female human embryonic stem cells.[1]"Human embryonic stem cells (hESCs) derived from inner cell mass (ICM) of blastocyst stage embryos have been used as a model system to understand XCI initiation and maintenance. Previous studies of undifferentiated female hESCs at intermediate passages have shown three possible states of XCI; 1) cells in a pre-XCI state, 2) cells that already exhibit XCI, or 3) cells that never undergo XCI even upon differentiation. In this study, XCI status was assayed in ten female hESC lines between passage 5 and 15 to determine whether XCI variations occur in early passages of hESCs. Our results show that three different states of XCI already exist in the early passages of hESC. "
References
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July 2010 "X Inactivation" - All (3157) Review (519) Free Full Text (1066)
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Cite this page: Hill, M.A. (2024, May 3) Embryology Molecular Development - X Inactivation. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Molecular_Development_-_X_Inactivation
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